U.S. patent application number 10/625627 was filed with the patent office on 2004-04-01 for linear electric machine.
Invention is credited to Hagiwara, Yasumasa, Yatsuzuka, Shinichi.
Application Number | 20040061384 10/625627 |
Document ID | / |
Family ID | 32024469 |
Filed Date | 2004-04-01 |
United States Patent
Application |
20040061384 |
Kind Code |
A1 |
Yatsuzuka, Shinichi ; et
al. |
April 1, 2004 |
Linear electric machine
Abstract
A linear electric machine includes a plurality of teeth spaced
apart from each other, a yoke magnetically connected to the teeth,
a plurality of coils mounted on the teeth and a movable core
disposed opposite the teeth to reciprocate relative to the teeth
along an axis of the movable core. The movable core has a plurality
of permanent magnets at axially opposite ends thereof for supplying
magnetic flux to the teeth, and a member for suppressing generation
of a magnetic field disposed at an axial center of the movable core
to magnetically separate the permanent magnets.
Inventors: |
Yatsuzuka, Shinichi;
(Chiryu-City, JP) ; Hagiwara, Yasumasa;
(Kariya-City, JP) |
Correspondence
Address: |
POSZ & BETHARDS, PLC
11250 ROGER BACON DRIVE
SUITE 10
RESTON
VA
20190
US
|
Family ID: |
32024469 |
Appl. No.: |
10/625627 |
Filed: |
July 23, 2003 |
Current U.S.
Class: |
310/13 |
Current CPC
Class: |
H02K 33/16 20130101 |
Class at
Publication: |
310/013 |
International
Class: |
H02K 041/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 26, 2002 |
JP |
2002-245180 |
Claims
What is claimed is:
1. A linear electric machine comprising: a plurality of teeth
circumferentially disposed to surround a space; a yoke disposed
around the teeth and magnetically connected to the teeth; a
plurality of coils mounted on the teeth; and a movable core
disposed in the space opposite the teeth to reciprocate
transversely to the teeth, said movable core having a plurality of
first permanent magnets at axially opposite ends for supplying
magnetic flux to the teeth; wherein said movable core comprises
means for suppressing generation of a magnetic field disposed to
magnetically separate the permanent magnets.
2. A linear electric machine comprising: a movable core disposed to
be able to reciprocate along an axial direction; a plurality of
magnetic teeth disposed to face the movable core; and a plurality
of coils mounted on the teeth; wherein said movable core comprises
magnetically shielding means for suppressing generation of a
magnetic field and a pair of permanent magnets respectively
disposed on the opposite sides of the shielding means in the axial
direction.
3. The linear electric machine as claimed in claim 2, wherein said
magnetic teeth extend perpendicularly to the axial direction of
said movable core.
4. The linear electric machine as claimed in claim 2, wherein said
magnetically shielding means is made of a non-magnetic
material.
5. The linear electric machine as claimed in claim 2, wherein said
magnetically shielding means comprises a second permanent magnet
that has opposite polarity to the first permanent magnets.
6. The linear electric machine as claimed in claim 2, wherein said
movable core further comprises a inductor made of magnetic material
disposed in a magnetic path between the first permanent magnets and
the teeth.
7. The linear electric machine as claimed in claim 2, further
comprising a plurality of magnetic inductors, wherein said first
permanent magnets are disposed around a center of a plane that is
perpendicular to the reciprocating direction of said movable core
and polarized in directions perpendicular to the reciprocating
direction, and said magnetic inductors are disposed between said
first permanent magnets in the direction perpendicular to the
reciprocating direction, and wherein a center line (L1) of each
said first permanent magnet in a radial direction inclines to a
center line (L2) of the teeth.
8. The linear electric machine as claimed in claim 7, wherein said
first permanent magnets project from said inductors to be located
between the adjacent teeth.
9. The linear electric machine as claimed in claim 7, wherein said
movable core has a magnet shielding member at the center of the
cross-section perpendicular to the reciprocating direction of said
movable core.
10. The linear electric machine as claimed in claim 2, wherein said
coils are connected to an ac power source to reciprocate said
movable core.
11. The linear electric machine as claimed in claim 2, wherein said
movable core is connected to means for reciprocating to generate
electric power at the coils.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] The present application is based on and claims priority from
Japanese Patent Application 2002-245180, filed Aug. 26, 2002, the
contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a linear electric machine
that moves back and forth along a straight line, such as a linear
motor, a vibrator or a linear generator.
[0004] 2. Description of the Related Art
[0005] U.S. Pat. No. 6,499,972 B2 discloses an actuator of a linear
compressor. The actuator is constituted of a movable core with a
plurality of circumferentially disposed permanent magnets on it, a
plurality of teeth disposed around the movable core and a plurality
of exciting coils respectively mounted on the teeth.
[0006] In the linear electric machine, the polarity of the
permanent magnets that are disposed opposite ends in the direction
of the linear motion has to be made different. The actuator of the
linear compressor disclosed in the US patent includes permanents
magnets disposed on the opposite ends of the movable core, which
are in contact with each other. Therefore, a considerable amount of
magnetic flux is confined in the movable core, and magnetic force
between the teeth and the movable core can not be sufficiently
generated. This lowers the efficiency of the linear electric
machine.
[0007] That is, a linear actuator or motor having the above
structure can not generate sufficient driving force, and a linear
generator having the above structure can not generate sufficient
electric power.
SUMMARY OF THE INVENTION
[0008] In view of the above described problem, a main object of the
invention is to provide an improved linear electric machine that
can provide sufficient driving force or electric power.
[0009] According to a main feature of the invention, a linear
electric machine includes a movable core that has a plurality of
first permanent magnets at axially opposite ends for supplying
magnetic flux to the teeth and means for suppressing generation of
a magnetic field disposed at an axial center thereof to
magnetically separate the permanent magnets.
[0010] According to another aspect of the invention, a linear
electric machine includes a movable core that includes magnetically
shielding means for suppressing generation of a magnetic field and
a pair of first permanent magnets respectively disposed on the
opposite sides of the shielding means in the axial direction.
[0011] Therefore, the magnetic flux of the permanent magnet can be
effectively utilized.
[0012] In the above linear electric machine, the magnetically
shielding means may be made of a non-magnetic material. The
magnetically shielding means may also be made of a second permanent
magnet that has opposite polarity to the first permanent
magnets.
[0013] The movable core may further include inductors made of
magnetic material disposed in magnetic paths between the first
permanent magnets and the teeth. 6. In this case, the first
permanent magnets are disposed around a center of a plane that is
perpendicular to the reciprocating direction of the movable core
and polarized in directions perpendicular to the reciprocating
direction. The magnetic inductors are disposed between the first
permanent magnets in the direction perpendicular to the
reciprocating direction. Preferably, a center line (L1) of each
first permanent magnet in a radial direction inclines to a center
line (L2) of the teeth. In the linear electric machine having the
above features, the first permanent magnets may project from the
inductors to be located between the adjacent teeth. The movable
core may have a magnet shielding member at the center of the
cross-section perpendicular to the reciprocating direction of said
movable core.
[0014] The coils of the linear electric machine may be connected to
an ac power source to reciprocate the movable core as a linear
motor. On the other hand, the movable core may be connected to
means for reciprocating the movable core to generate electric power
at the coils.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Other objects, features and characteristics of the present
invention as well as the functions of related parts of the present
invention will become clear from a study of the following detailed
description, the appended claims and the drawings. In the
drawings:
[0016] FIG. 1 is a schematic diagram illustrating a pulse tube type
cooling machine to which a linear electric machine according to the
invention is applied;
[0017] FIG. 2A is a cross-sectional view of the linear electric
machine cut along line II-II in FIG. 1 and FIG. 2B is a cross
sectional side view of the linear electric machine cut along line
IIB-IIB in FIG. 2A;
[0018] FIG. 3 is a schematic diagram illustrating a main feature of
the linear electric machine according to the first embodiment of
the invention;
[0019] FIG. 4A is a perspective view of a movable core of the
linear electric machine according to the first embodiment of the
invention, and FIG. 4B is a cross sectional view of the movable
core;
[0020] FIGS. 5A and 5B are schematic perspective views of a spacer
of the linear electric machine according to the second embodiment
of the invention;
[0021] FIG. 6A is a schematic cross-sectional plan view of a linear
electric machine according to the third embodiment of the
invention, and FIG. 6B is a perspective view thereof;
[0022] FIG. 7A is a schematic cross-sectional plan view of a linear
electric machine according to the fourth embodiment of the
invention, and FIG. 7B is a cross-sectional side view thereof;
[0023] FIG. 8 is a schematic cross-sectional plan view of a
modification of the linear electric machine according to
invention;
[0024] FIG. 9 is a schematic cross-sectional plan view of a
modification of the linear electric machine according to
invention;
[0025] FIG. 10 is a schematic cross-sectional plan view of a
modification of the linear electric machine according to invention;
and
[0026] FIG. 11 is a schematic diagram illustrating a generator
driven by a thermoacoustic engine.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] A linear electric machine according to the first embodiment
of the invention, which is applied to an actuator of a linear
compressor for a pulse tube type cooling machine, will be described
with reference to FIGS. 1-4. As disclosed in U.S. Pat. No.
6,499,972 B2, the pulse tube type cooling machine includes a
radiator 1, a heat accumulator 2, a heat extractor 3, a pulse tube
4, a capillary tube 5, a buffer tank 6, a linear compressor 10,
etc. The linear compressor 10 includes a cylinder 11, a piston 12
disposed in the cylinder 11 and an actuator 13 that reciprocates
the piston 12 along the inside surface of the cylinder 11.
[0028] The actuator 13 includes a movable core 14 that is disposed
to move back and forth on a line of reciprocation, a plurality of
magnetic teeth 15 that extends in the radial direction
perpendicular to the line of reciprocation, a plurality of solenoid
coils 16 respectively mounted on the teeth 15, a leaf spring 17
that supports the movable core 14 and a casing 18 that accommodates
the above described parts or components. The casing 18 is a
pressure vessel made of stainless steel. The piston 12 and the
movable core 14 are connected by a non-magnetic shaft 19 that
penetrates the movable core 14 in the axial direction thereof or in
the direction of motion of the movable core 14. The solenoid coil
16 is constituted of a resinous non-magnetic bobbin and a
conductive coil made of copper or aluminum.
[0029] A plurality (e.g. four) of the teeth 15 are disposed around
the generally columnar movable core 14 to protrude radially inward
from an annular yoke 20, as shown in FIG. 2A. The teeth 15 and the
yoke 20 are constituted of laminated magnetic plates such as
magnetic iron sheets or permendur sheets to form magnetic paths of
the magnetic flux induced by the solenoid coil 16. The laminated
magnetic plates are disposed so that the lamination direction
thereof can be parallel to the direction of motion of the movable
core 14. In other words, the movable core 14 and the teeth 15 are
disposed so that the lamination directions thereof can be parallel
to each other.
[0030] As shown in FIG. 2B, the movable core 14 includes a magnet
shielding plate 14a, a plurality (e.g. 8) of permanent magnets 14b
and a plurality (e.g. 8) of inductors 14c. The permanent magnets
14b are equally disposed on the opposite sides of the shield plate
14a. The magnet shielding plate 14a is made of non-magnetic
material, such as stainless steel, copper and aluminum to prevent
the magnetic flux of the permanent magnets from being confined in
the movable core 14. In other words, the magnet shielding plate 14a
increases effective magnetic flux supplied from the permanent
magnets 14b to the teeth 15. The permanent magnets 14b are made
from neodymium-iron alloy, samarium-cobalt alloy or ferrite. The
permanent magnets 14b are disposed so that the center lines L1 of
the permanent magnets 14b in the radial direction can incline to
the center lines L2 of the teeth 15, as shown in FIG. 3, and
magnetized so that the lines of the magnetic force can be
perpendicular to the direction of the motion of the movable core
14. The inclination angle between the center line L1 and the center
line L2 is 360 degrees/the number (4) of the teeth/2, or 45
degrees. One of the permanent magnets 14b disposed on one side of
the magnet shielding plate 14a is magnetized to have the polarity
opposite to the polarity of an adjacent permanent magnet 14b
disposed on the other side.
[0031] As shown in FIGS. 4A and 4B, each one of the inductors 14c
is constituted of radially arranged magnetic plates disposed in a
quarter section of the columnar movable core 14 that are
respectively divided by the permanent magnets 14b. Each plate lies
so that the rolled surface thereof can be approximately in parallel
to the direction of motion of the movable core 14. The magnetic
plates are made of the same material as the teeth 15, such as
magnetic iron sheets or permendur sheets. Therefore, the magnetic
flux mainly flows from the permanent magnets 14b through the
inductors 14c to the tooth 14.
[0032] The movable core 14 has a magnet shielding center hole 14d
at the center of the cross-section thereof perpendicular to the
direction of motion thereof. The shaft 19 is made of non-magnetic
material, such as stainless steel, copper or aluminum, and is
force-fitted to the center hole 14d. Each of the magnetic plates
disposed around the center hole 14d are arranged to be
perpendicular to the direction of motion of the movable core 14.
The magnet shielding center hole 14d increases the effective
magnetic flux supplied to the teeth 15 from the permanent magnets
14b.
[0033] The solenoid coil 16 is applied an output voltage of a
electronically control unit, which cyclically changes the magnetic
polarity of the teeth 15 at a frequency corresponding to the
natural vibration frequency caused by the elasticity of the movable
core 14, the leaf spring 17 and working fluid. Accordingly, the
attractive and repulsive forces, which are exerted between the
teeth 15 and the movable core 14, are cyclically reversed to
reciprocate the movable core 14.
[0034] The movable core 14 and the teeth 15 are disposed so that
the permeance between the movable core 14 and the teeth 15 becomes
a maximum when the piston 12 is located at the middle (the center
of vibration) between the top dead center and the bottom dead
center. In other words, the thrust of the movable core 14 becomes
the maximum at the middle or the center of vibration.
[0035] A linear electric machine according to the second embodiment
of the invention will be described with reference to FIGS. 5A and
5B.
[0036] As shown in FIG. 5A, the magnet shielding plate 14a is made
of a permanent magnet instead of a non-magnetic material. The
permanent magnet shielding plate 14a is magnetized to have the
polarities opposite to the polarities of the permanent magnets 14b
that is shown in FIG. 4A.
[0037] The magnet shielding plate 14a may be constituted of a
non-magnetic plate and a plurality of permanent magnet bars 14a'
that are embedded into the non-magnetic plate and magnetized to
have the polarities opposite to the polarities of the permanent
magnets 14b, as shown in FIG. 5B.
[0038] The magnet shielding plate 14a, or 14a' that is constituted
of a permanent magnet or a plurality of permanent magnets increases
the effective magnetic flux of the movable core 14, so that the
thrust of the movable core 14 can be significantly increased.
[0039] A linear electric machine according to the third embodiment
of the invention will be described with reference to FIGS. 6A and
6B. Incidentally, the same reference numeral that indicates a part
or component of the following embodiments as the previous
embodiment will indicate the same or substantially the same part or
component, hereafter.
[0040] As shown in FIGS. 6A and 6B, the radially outer portion of
each permanent magnets 14b projects from the inductors 14c of the
movable core 14 to be located between the adjacent teeth 15.
[0041] Therefore, the size of the permanent magnets 14b can be
increased so that the effective magnetic flux of the permanent
magnets 14b or the thrust of the movable core 14 can be increased
without increasing the total volume of the actuator 13.
[0042] A linear electric machine according to the fourth embodiment
of the invention will be described with reference to FIGS. 7A and
7B.
[0043] The movable core 14 is constituted of four arc-shaped
permanent magnets 14b that are disposed at the peripheral portion
of the movable core 14 and four arc-shaped inductors 14c that cover
the outer surfaces of the permanent magnets 14b. Numeral 14e
indicates a longitudinal magnet shielding groove.
[0044] Various modifications of the linear electric machine
according to the invention will be described with reference to
FIGS. 8-11.
[0045] The above described linear electric machines can be utilized
as a generator, as shown in FIGS. 8-10. FIG. 11 shows a
thermoacoustic engine for reciprocating the movable core 14 of the
generators shown in FIGS. 8-10.
[0046] In the foregoing description of the present invention, the
invention has been disclosed with reference to specific embodiments
thereof. It will, however, be evident that various modifications
and changes may be made to the specific embodiments of the present
invention without departing from the scope of the invention as set
forth in the appended claims. Accordingly, the description of the
present invention is to be regarded in an illustrative, rather than
a restrictive, sense.
* * * * *